0 Guidelines for safe MR practice MRI SafetyGuidelines for safe MR practiceCatalyst Imaging Consortium
1 OutlineIntroductionSafety concerns-practicing safe imagingDistress in MRI environmentPatient and visitor screeningReal situationsEthical conductReferences
2 IntroductionMagnetic Resonance Imaging (MRI) has been in use for over two decades and is viewed as a medical procedure associated with acceptable and well controlled risks.However, there are potential risks in the MRI environment.This document is a compilation of the MR safe practice guidelines from the following institutions:BIDMC, BWH, CHB, DFCI, MIT and MGH.
3 The MRI system The MRI system uses 3 types of magnetic field: Large superconducting magnet producing main magnetic field.High field magnets are 1.5T or 3TFor comparison, 1.5T = 25,000 times the magnetic field of the earthRadio Frequency field (RF)RF signal is transmitted to excite hydrogen protons in the patient. These protons give a signal in returnRF transmission can affect electronic devicesGradient magnetsSmaller magnets, used to alter the main magnetic field and allow the signal from the patient to be spatially encoded into a pictureThey are turned on/off very quickly during scanning, causing the knocking noise associated with MRI
4 MRI site restriction access MRI site divided in 4 zones:Zone I: Waiting areasafe, freely accessibleZone II: Initial contact:semi-restricted, interface between uncontrolled zone I and strictly controlled zones III and IVzone where patients are screenedZone III: Control room:access strictly restricted, directly connected to zone IV, screening before enteringZone IV: Magnet room:Access restricted, free access might result in serious injury
6 Projectile/Missile Effects The most immediate danger associated with the environment is the attraction between the magnet and ferromagnetic metal objects.Those objects can become airborne projectilesEven hand-held objects can be jerked free very suddenly as the holder moves closer to the magnetRemember, even when you are not scanning, the magnet is not "off". NEVER bring any metal objects into the scanner rooms.
7 Implanted DevicesPacemakers, cardiac defibrillators, medication pumps, nerve stimulator devices and other devices can be affected by the magnetic field.Pacemaker wires alone are also contraindicatedCardiac pacemakers: magnets may induce arrhythmias, bradycardias, tachycardiaAneurysm clips:Need document that prove that they are MR safeArtifacts, even with safe clipsHeart Valve:Most are safe but positive documentation must be obtainedMany have been evaluated and showed mild rotation torque on the system. But, theses forces are minimal compared to the force exerted by the beating heart
8 Metal in the body Torque and Heating: Some metallic implants can show considerable torque.The force exerted can be considerable.factors: type/degree/mass & geometry of object.Non-ferrous metallic objects may show little or no deflection, but could still heat.In addition, metal in or near the body (such as dental implants) can produce artifacts, which adversely effect image quality.
9 Nerve stimulationBy Faraday’s law of induction: exposure of conductive tissue to time-varying magnetic fields will induce an electric field.The induced current is greater in peripheral tissue (amplitude of the gradient is highest farther away from the magnet's isocenter)Nerve stimulation leads to mild skin sensations and involuntary muscle contractionsPatients should not have their hands clasped, it creates a closed loop, and can induce nerve stimulation. The person’s hands should be positioned by their side. The ankles should not be crossed eitherMagnetophosphenes: visual sensation of flashes of light due to retina stimulation
10 Auditory issuesStrong, static magnetic field in conjunction with current pulse to create gradient magnetic fields produce mechanical forces and motion. The result is acoustic noise.Study showed temporary hearing loss in 43% of subjects (Brummett et al, 1988)Patients should always be given noise reducing protection , in the form of earplugs or headphones during scanning
11 Thermal HeatingTransmitting radio-frequency electromagnetic energy into body tissues causes energy dissipation in the form of heat.Absorption of RF power is described in terms of Specific Absorption Rate (SAR) in Watt/kg.Greatest effects at periphery or surface of the body.Scanner determinants: RF frequency, type of RF pulse, TR (repetition time) and total RF numbers per TR.Body determinants: thermoregulatory function.
12 Thermal HeatingThe safety standards are designed to ensure that no tissue is subjected to a temperature increase of over 1°C.4 Watt/kg averaged over the whole body for any 15-minute period (1.5 Watt/kg if patient is thermally compromised, as a function of room temperature and humidity)3.2 Watt/kg averaged over the head for any 10-minute periodGuidelines for industry and FDA staff, found at
13 Electrical burnsRF fields can cause burns by producing electrical currents in conductive loops.Only minor temperature changes reported in implanted devices (Yeung et al, 2002)Transdermal patches with metallic backing must be removed (FDA warning 03/09)“Red Dot” ECG leads must be removedLooped ECG leads, pulse oximeter cables, etc. can cause burnsDark tattoos may cause heatingRef: Yeung et al, 2002 modeling of RF energy due to metal implants in MRIFound at:http://www.bme.jhu.edu/~yeung/Yeung_IEEEAPS_2002.pdf
14 What is a quench? Rapid loss of magnetic field, 20-30 seconds. Occurs when the liquid cryogens boil off rapidlyCan occur via manual activation (quench button) or spontaneously by a fault in the magnet itselfA quench should ONLY be performed by authorized personnel with proper training in dire emergency that involves a serious personal injury. Sudden loss of the magnet field in a quench situation could damage the magnet or components of the system. There is a considerable cost related to quenching the magnet and re-implementing the magnetic field.Ref:
15 Quench In the event of a quench. Evacuate all persons from the magnet roomVenting of liquid cryogens may cause a loud bang / thundering / hissing / rushing sound with the cold gas expulsion.In the process of a quench.If venting system fails, cryogens will fill scanner room pressure potential ear drum ruptureAsphyxiation can occur from breathing helium. Oxygen is displaced.Hypothermia & frostbite can occur due to the extremely cold helium, the temperature of liquid helium is approximately -269 degrees C or 4.17 degrees K.
16 Reaction to contrast agent Anaphylactic reactions are rare but do occur.In case of severe reaction, administration of epinephrine with auto injector device (0.5 mg of 1:1000 concentrated epinephrine to be given intramuscularly in the lateral thigh, lower dose for people under 50 kg)The auto injector should be within easy reach, for example in an emergency tackle box
17 Nephrogenic systemic fibrosis (NSF) & Gadolinium NSF is a newly discovered disease (1997) that has been associated with the use of gadolinium-based MRI contrast agents in patients with severe renal disease, most commonly those on dialysisNSF is a disorder characterized by thickening and hardening of the skin and immobility or tightening of the joints.If the patient has risk factors for kidney disease (> 60 years, diabetes, systemic lupus erythematosis, history of renal disease, multiple myeloma), a BUN/creatinine should be performed within 1 month of examination (lab value cutoffs may be institutionally determined)
18 Nephrogenic systemic fibrosis (NSF) & Gadolinium It is advisable that no patient with an eGFR of <30 ml/min/m2 (Stage 4 or 5 kidney disease) should receive Gd contrast agents unless the benefits are deemed to outweigh the risksConsultation with a radiologist is suggested before administrating Gd contrast agents to a pediatric patient or a patient with a eGFR of <60 ml/min/m2No radiologist consent needed eGFR >60
19 Pregnancy No known adverse effects of MRI on developing fetuses Research:Given the scarcity of data on the subject and the high susceptibility of the developing fetus to damage in general, it is not worth the risk for pregnant women to participate as subjects in MR research studiesMRI technologists:Most clinical units allow pregnant employees to enter the scan room, but not to remain in the room while the RF and gradient fields are applied during image acquisition.
20 PregnancyClinical:MRI used to evaluate obstetrical, placental, and fetal abnormalities in pregnant patients for more than 20 years. It is recognized as a beneficial diagnostic tool and is utilized to assess a wide range of diseases and conditions that affect the pregnant patient as well as the fetus.Overall decision to utilize an MRI procedure in a pregnant patient involves answering a series of important questions including, the following: Is sonography satisfactory for diagnosis? Is the MR procedure appropriate to address the clinical question?Is obstetrical intervention prior to the MR procedure a possibility? That is, is termination of pregnancy a consideration? Is early delivery a consideration
21 Pregnancydiagnostic technique should not be withheld for the following cases: Patient with active brain or spine signs and symptoms requiring imaging. Patients with cancer requiring imaging. Patients with chest, abdomen, and pelvic signs and symptoms of active disease when sonography is non-diagnostic. In specific cases of suspected fetal anomaly or complex fetal disorder.Ref: MRIsafety.com
22 Pregnancy Contrast agents and pregnancy Studies of gadolinium-based MRI contrast agents in pregnancy have been limited, and effects on the embryo or fetus are unknown.Gadolinium-based MR contrast media cross the human placenta and into the fetus when given in clinical dose rangesMR contrast agents should not be routinely provided to pregnant patients. This decision, is one that must be made on a case-by-case basis after assessing the risk-benefit ratio for the particular patientIt is recommended that pregnant patients undergoing an MR examination provide written informed consent to document that they understand the risks and benefits of the MR procedure to be performed, are aware of the alternative diagnostic options available to them (if any), and wish to proceed.
23 Pediatric MRI Sedation and monitoring Screening issues Largest group requiring sedation because of inability to remain motionless.Sedation protocol subject to institution reviewNeonatal and young pediatric population, special attention needed in monitoring body temperatureMR compatible equipment commercially available (warming devices, monitoring, incubator)Screening issuesChildren may not be reliable, should be questioned both in presence of parents/guardians and separatelyStuffed animals and other comfort items represent real risk. Some facilities have a choice of safe toys for kid to choose during scanning time
24 Distress in the MRI environment Incidence of distress among clinical MRI is highDistress can be caused by many factors including: confined space, noise, restriction of movementDistress can range from mild anxiety to full blown panic attackDistress can result in subject motion and disrupt image quality
25 Distress in the MRI environment Minimizing subjective distressCareful screeningComplete explanations on the aspect of the MR examinationMake them comfortable in the scannerMaintain verbal contactGive them the panic button
26 Patient and visitor screening All persons undergoing an MRI examination, regardless of their medical conditions, must either complete the screening form or have one completed by a relative/healthcare proxy.Conditions that rule out a patient/subjectCardiac pacemakerSurgical aneurysm clipsNeurostimulatorImplanted pumpsMetal in body/eyes. Patient must be cleared by a radiologist (usually via routine Xray)Pregnancy (for research)
27 Patient and visitor screening Conditions that might rule out a patient/subject:Ear implants (most are OK, certain cochlear implants are not)Metal rods, plates or screws in body or mouthPrevious surgery (if metal left in body)IUD (most are OK except Copper-7)Hearing aid (should be removed)Dentures (should be removed)Prosthetic heart valve (most are plastic now)Braces (causes severe frontal artifact)Hair extensionsTattoos or permanent eyeliner (if ink contains metallic specks)
28 Patient/subject preparation Individuals undergoing an MRI exam must remove the following:Jewelry, even if pure gold. Exception wedding bands which cannot be removed.Hearing aidsBody piercingWatchesHair holderMetal on clothing (belt, metal buttons, underwire bra)Any magnetic media (credit card), electronic devices (cell phones, beepers,…) will be damagedMost hospitals required patient/subject to change into a hospital gowns
29 Prior MRI scansDo not consider the individual’s history with prior scans as a reason to bypass screening. Exception: patient was scanned within 24 hours (or within the same day), and screening form is accessible.
30 Real situationsYou suddenly discover the patient has a ferrous magnet clip and the patient is already in the scanner:Remove the patient slowly from the systemA metal worker has had several MRI’s from outside institutions:You still need documentation that there is no metal presence in the eyes. Must obtain orbits prior to imaging.An IV pole is inside the bore, but no one is hurt:You should immediately call service. In trying to remove the object you can cause harm to yourself and/or another individual
31 Real situations Medical emergency: No resuscitation equipment can be brought in the magnet roomInitiate basic life support or CPR as required by the situation while the patient is being emergently removed from Zone IV to a predetermined, magnetically safe locationTo move the patient from magnet room to holding area, undock the table (if possible) or use a MRI compatible stretcher to move the patientCall emergency personnel
32 Ethical conduct Investigator training Responsibility of every investigator/clinician to be fully informed about and to practice current standards of good clinical practiceUnderstanding of requirements for obtaining true informed consent.Critical elements to informed consentNo element of coercion in the recruitment of research subjectsAll risks must be clearly specified in the consent.
33 Ethical conduct Risk/benefit considerations Research: the investigator must demonstrate how the outcome of the study will directly impact the clinical care of that study population. This is true not only for clinical trials of potential new treatments, but also for pharmaceutical challenge studies.Each investigator to determine all potential risks or adverse outcomes from a proposed study and to establish that the benefit to society will sufficiently outweigh the risk to the participating individuals.
34 Current FDA Criteria for non-significant risks Field strength < 8T for anyone aged one month and olderSAR < 3 W/kg averaged over 10 minutes in headSAR < 8 W/Kg in any 1 cc of tissue in head averaged over 5 minutesAcoustic Noise <140 dB peak and 99 dB average with ear protectionNo painful or severe peripheral nerve stimulation
35 ACR blue ribbon panelThe first American College of Radiology white paper on MR safety appeared in the June 2002 issue of the AJR. This first report was produced by a blue-ribbon panel of experts chaired by Emanuel Kanal, MD, and covered all areas related to MR safety. A second version of the report, which appeared in the May 2004 issue of the AJR, provided an update and revisions. The current report is the product of a significantly expanded panel of experts that includes academic and community practice radiologists and representatives of anesthesiology, cardiology, medical physics, MR technology, MR nursing, architecture, legal counsel, the Food and Drug Administration, and numerous related disciplines. Dr. Emanuel Kanal again serves as the chair of this distinguished panel.Included are recommendations on imaging pregnant patients, pediatric screening and sedation issues, the safety of accompanying family or personnel, and relevant physical principles associated with high magnetic fields, to name a few. The section on MR contrast agent use is very current, including information on the association of certain gadolinium-based MR contrast agents with the recently described nephrogenic systemic fibrosis in patients with impaired renal function.
36 References www.mrisafety.com List with information for over 1,200 implants, devices, materials and products (over 200 tested at 3T)
37 References Protection of human subjects Belmont reportTitle 45 Code of Federal Regulations Part 46 Protection of Human Subject
38 This presentation was done with the support of the Translational Technologies and Resourcesprogram of Harvard Catalyst | The Harvard Clinical and Translational Science Center(NIH Grant #1 UL1 RR and financial contributions from participating institutions).